Leakage reactance transformer



Oct. 11, 1966 A. R. COLLUCCI 3,278,878

LEAKAGE REACTANCE TRANSFORMER Filed Jan. 27, 1964 H604 FIG.5

ANTHONY R. COLLUCCI INVENTOR ATTORN EY United States Patent 3,278,878LEAKAGE REACTANCE TRANSFORMER Anthony R. Collucci, Ipswich, Mass.,assignor to Sylvauia Electric Products Inc., a corporation of DelawareFiled Jan. 27, 1964, Ser. No. 340,397 2 Claims. (Cl. 336--160) Thisinvention relates to apparatus for starting and operating electricdischarge lamps, particularly those of the igh pressure mercury typecontaining added metals and iodine. The apparatus will, however, beuseful with other devices which require similar characteristics.

Apparatus for starting and operating discharge lamps is generally calleda ballast and includes a transformer and inductive reactance, the lattergenerally being provided as leakage reactance. The lamp will start onthe open circuit voltage of the transformer, and the operating currentwill be limited by the reactance, causing a voltage drop which lowersthe voltage across the lamp. This is desirable, because the operatingvoltageof the lamp is generally much less than the starting voltage.

Various expedients have been used to increase the ratio of startingvoltage to operating voltage, but these have had disadvantages such asproducing a poor current wave form or requiring additional components,such as condensers.

With the use of iodine-containing mercury lamps, the problem becamegreater, because an even higher ratio of peak starting voltage toroot-mean-square operating voltage was necessary, and a considerableamount of energy had to be available at the peak of the starting voltagewave. The starting voltage, that is the open-circuit voltage of thetransformer, not only had to have a high peak in its wave form, but thepeak had to be maintained long enough over the cycle to supply enoughenergy to heat the electrodes sufiiciently and excite the gas. The peakvoltage could not be just instantaneous; it had to supply enough energyto maintain the discharge until proper conditions were established foran arc to occur. This takes longer in an iodine-containing lamp than inmy high pressure mercury lamp, which is more easily triggered intooperation. I

I have found that the starting of such lamps can be accomplished by theuse of a transformer in which a reg-ion of increased flux density asprovided in the series magnetic circuit of the transformer core byspacing the ends of at least some of the laminations, at the regionwhere they are ordinarily interleaved, a considerable distance apart,but having some other laminations extend across the gap between the endsof the first mentioned laminations. In this way, the flux density in theportion of the laminations which bridge the gap, is considerablyincreased, with consequent saturation effects.

However, the exact reason why these staggered gaps increases the ratioof peak open-circuit voltage to rootmean-square (R.M.S.) open-circuitvoltage, and provide other desirable effects, is not clear, and I do notwish to be limited to any theory in that respect.

Further objects, advantages, and features of the invention will beapparent from the following specification, taken in connection with theaccompanying drawing, in which:

FIG. 1 is a perspective view of a transformer according to theinvention;

FIG. 2 is an enlarged longitudinal section of the core in the vicinityof the air gaps;

FIG. 3 is a schematic circuit diagram of the electrical connections;

FIG. 4 is an oscillogram of the wave-form of the opencircuit voltage ofthe transformer; and

FIG. 5 is an oscillogram of the wave-form erating current in the lampcircuit.

of the op- 3,278,878 Patented Oct. 11, 1966 In FIG. 1, the rectangularcore 1 is made of lamina-,

tions bent into the form shown, preferably as shown in! Biggs et a1.United States Patent 3,096,568, issued July 9, 1963. They are made intooppositely-facing U-shaped sets, and joined together as in thatapplication, except for one very important difference: instead of theopen ends of the U being wholly interleaved where they join, in thepresent device only a relatively few strips are interleaved, and most ofthe strips in each U are spaced apart to form an air gap.

As shown in the comparatively enlarged view of FIG. 2, four strips 6, 7,8, 9 are spaced from strips 10, 11, 12, 13 to form such an air gap 14,and then the ends of strips 15 and 16 meet in a butt joint 17 betweenstrips 13 and 19 beyond the air gap. Strips 21, 22, 23, and 24 arespaced from strips 19, 25, 26, 27 to form air gap 28, which is bridgedby strips 29 and 30 which meet in a butt joint 31 beyond the air gap 28.Succeeding sets of strips can follow the same pattern, until the desiredthickness of core is achieved. In this way an air gap is provided andbridged by a few strips such as 29, 30 which will not only operate athigh flux density in the saturation range but will also form a structurewhich will hold together mechanically because of the interleavedbridging strips.

Returning now to FIG. 1, the rectangular core 1 is seen to have fourlegs 3, 4, 5, 2. A primary coil 40 and a secondary coil 41 encircle leg3, being spaced apart on that leg, which is much longer than legs 2 and4. Similarly, primary coil 42 and secondary coil 43 encircle leg 5, onwhich they are placed and spaced apart.

The magnetic shunts 44 and 45 extend from leg 3 to leg 5 outside core 1and between primary coils 40, 42, and the secondary coils 41, 43, thestrips or laminations 46 running perpendicularly to the side of thecore, as in copending US. patent application Serial No. 119,495, filedJune 26, 1961, now abandoned, by Sheppard Cohen, and assigned to thesame assignee as the present application.

The ends 47, 48 of the laminations of shunt 44 are welded in a lineabout inch wide across the ends of the strips as shown by the weld 49,and an additional weld 50 is similarly made on the side 51 of the shunt,and a hole drilled close to the weld about 43 inch from the weld in thespecific example described. A bolt 53, of which head 52 is shown, ispassed through the hole and secured on the other side of shunt 45, whichis similar to shunt 44 and similarly drilled by a nut. In the exampledescribed, bolt 53 can be a /2 inch bolt. The shunts 44 and 45 arecomposed of a series of fiat rectangles of transformer steel attached asshown. They do not penetrate into the opening, generally called thewindow, in the rectangle of the core 1.

The air gaps 14, 28 and so forth, as shown in FIG. 2, are in the core atabout the middle of the lengths of secondary coils 41, 43. This meansthat the U-shaped stack of strips having leg 2 as the bottom of the U isshorter than the stack having leg 4 at the bottom of its U.

The connection of the coils to the lamp are shown in FIG. 3. The twoprimaries 40, 42 are shown in parallel; in the transformer of thespecific example they would ordinarily be connected in parallel for1l5-volt operation, in series for 230-volt operation. Both secondaries41, 43, would be connected in series, in either case, and they wouldalso be in series with the two coil primary in the usualauto-transformer manner. The transformer is de signed for a frequency of60 cycles per second. A condenser 60, of about 28 microfarads in theexample de scribed, is also in series with the lamp 61, which ispreferably a high-pressure arc discharge lamp with a filling of mercuryvapor, iodine vapor, and other metals, for example, thorium.

In an example of the invention, primary coils 40, 42 were each of 378turns of #16 B. & S. enamelled copper wires, there being 38 turns perlayer. Secondary coils 41, 43 were of 275 turns of #19 B. & S. wire ofthe same kind, with 20 turns per layer. If these coils are connected asin FIG. 3, this gives an auto-transformer turns ratio \of 1031/275, andsince the open-circuit peak voltages in ithis transformer are found tocorrespond closely with the ,turns ratio although the operating voltageis much lower, than for a primary R.M.S. voltage of 120 volts, theprimary peak will be about 169 volts, and the secondary peak about 650volts, as indicated in FIG. 4. The operating voltage of the transformerwill be much lower, about 290 volts.

In the specific example, the outside dimensions of the main core 1 areabout inches along leg 3, and about 2 5 along leg 2, and about 2% incheswidth of each strip. The legs are A inch thick from the outside strip tothe inside strip. The bridged air gaps are about 1% inches from theoutside end of the core, and the strips are welded together in positionsabout /2 inch on either side of each air gap. The welds like those onthe shunts 44 and 45 are bead-welded to a depth into the core of aboutinch. The legs include about 44 strips each of about #26 gauge, that is,each being about 18 /2 mils thick, about 8 of the laminations bridging aW inch airgap to bridge it across, as previously stated. The exactnumber of laminations may vary slightly because of diflferences in thethickness of the commercial strip from piece to piece. In this specificexample, at least 8 of the laminations had to be interleaved to give theright transformer characteristics.

A metal band will generally be fastened, by welding or in some othersecure manner, to the outside of the core.

The steel strips of which the core is made should be of silicon steel asused for transformers, the silicon contact generally being about 4%.

In this application, the words strip and laminations are usedinterchangeably since the laminations of the core are steel strips. Thewords airgaps and-gap are used interchangeably, since a gap in themagnetic core is customarily called an airgap, even if it is filled withnonmagnetic material, such as fibre or a resin.

After the transformer is assembled, it can be impregnated or coated witha protective varnish in the usual manner.

What I claim is:

1. A transformer having a four-legged main magnetic core, the legsarranged to form a rectangle having a window, two of the legs being longand two short, a primary coil and a secondary coil on each long leg, thesecondary coils being connected in series aiding the primary andsecondary coils on each leg being spaced apart, a magnetic leakage shuntextending from one long leg to the other in the space between coils, anda partially bridged gap in the portion of each long leg inside asecondary coil, the gap being formed by laminations whose ends arespaced apart from each other and bridged by laminations which extendacross the gap to meet corresponding laminations in a butt joint beyondthe air gap and interleaved with the other laminations.

2. The transformer of claim 1, in which the number of interleavedlaminations which meet in gaps is about 20% of the number which meet inbutt joints.

References Cited by the Examiner UNITED STATES PATENTS 2,350,029 5/1944Glass 336-212 X 2,353,511 7/1944 Short 336-234 X 2,550,501 4/1951 Sims336--178 X 2,553,591 5/1951 Kronmiller 336165 X 2,553,596 5/1951 Mann336-165 X 2,762,988 9/1956 Pomazal et a1 336212 X 2,830,277 4/1958 Kane336234 X 2,850,708 9/1958 Antalis 336 X 3,128,443 4/1964 Herman et a1336- X LEWIS H. MYERS, Primary Examiner.

ROBERT K. SCHAEFER, Examiner.

T. J. KOZMA, Assistant Examiner.

1. A TRANSFORMER HAVING A FOUR-LEGGED MAIN MAGNETIC CORE, THE LEGS ARRANGED TO FORM A RECTANGLE HAVING A WINDOW, TWO OF THE LEGS BEING LONG AND TWO SHORT, A PRIMARY COIL AND A SECONDARY COIL ON EACH LONG LEG, THE SECONDARY COILS BEING CONNECTED IN SERIES AIDING THE PRIMARY AND SECONDARY COILS ON EACH LEG BEING SPACED APART, A MAGNETIC LEAKAGE SHUNT EXTENDING FROM ONE LONG LEG TO THE OTHER IN THE SPACE BETWEEN COILS, AND A PARTIALLY BRIDGED GAP IN THE PORTION OF EACH LONG LEG INSIDE A SECONDARY COIL, THE GAP BEING FORMED BY LAMINATIONS WHOSE ENDS ARE SPACED APART FROM EACH OTHER AND BRIDGED BY LAMINATIONS WHICH EXTEND ACROSS THE GAP TO MEET CORRESPONDING LAMINATIONS IN A BUTT JOINT BEYOND THE AIR GAP AND INTERLEAVED WITH THE OTHER LAMINATIONS. 